Not applicable.
The present invention generally relates to electrically insulating polymeric compositions that are suitable for use as adhesives, potting compounds and encapsulating materials for electronic devices. More particularly, this invention relates to an electrically-insulating polymer-base material with enhanced thermal conductivity so as to be particularly suitable for heat management of electronic devices.
Heat generated by electronic devices during normal operation can cause overheating and device failure if not adequately conducted away. Steady-state heat can be removed from the device and dissipated to the surrounding environment by the manner in which the device is mounted to its supporting structure and the use of heat sinks that conduct and/or dissipate the heat. For example, it is standard practice to attach an integrated circuit (IC) chip and other power-dissipating devices directly to a heat sink. Many heat sinks are electrically conductive, and therefore must be electrically insulated from the device to prevent shorting of electrical signals. For this reason, device attachment is often with an electrically insulating adhesive, which typically comprises an adhesive resin mixed with thermally-conductive dielectric filler particles, such as ceramics including alumina (Al2O3), aluminum nitride (AlN) and boron nitride (BN). In this manner, the low thermal conductivity of the resin (e.g., about 0.23 W/mxc2x0 C.) is raised by the ceramic filler material (e.g., about 40 W/mxc2x0 C.). However, the thermal conductivities of ceramic materials are much lower than metals such as copper (about 395 W/mxc2x0 C.) and other highly thermally-conductive materials.
With an ever-increasing need for more efficient heat removal from high power electronic devices, traditional thermally conductive adhesives are not adequate for many applications. Accordingly, it would be desirable if an electrically-insulating adhesive having improved thermal conductivity was available. It can be appreciated that for an electrically-insulating adhesive to be suitable for a wide range of applications in electronic products, the material should also be relatively low cost, have a low ionic content for corrosion resistance, exhibit acceptable voltage breakdown, and undergo minimal material property changes after long term exposure to the operating environment.
The present invention provides an electrically-insulating polymer-based material with improved thermal conductivity so as to be suitable for use as an adhesive for mounting and conducting heat from electronic devices. The material is also suitable for use as a potting compound and an encapsulation material for various electronic applications. The polymer-based material comprises a polymer matrix material in which are dispersed metal particles that are individually encapsulated by a dielectric coating so that the metal particles are electrically insulated from each other. The dielectric coating is insoluble in the matrix material so that the electrical insulation provided by the coating between particles does not degrade. In a preferred embodiment, the polymer-based material also comprises dielectric particles dispersed in the matrix material and/or the dielectric coating for the purpose of further increasing the thermal conductivity of the polymer-based material.
To yield a thermally stable material, the metal particles preferably have a melting temperature well above the maximum operating temperature of the electronic device with which the polymer-based material is used, i.e., contacts, bonds, encases, etc. For example, the metal particles may be formed of such electrically-conductive metals as copper, aluminum and/or silver. The dielectric coating has a softening temperature that is higher than the maximum operating temperature of the electronic device, but can be well below the melting temperature of the metal particles. As a result, both the metal particles and the dielectric coating are stable throughout the operating temperature range of the electronic device with which the polymer-based material is used. Suitable matrix materials for the polymer-based material of this invention are electrically nonconductive, and are preferably capable of stopping ionic intrusion, have low ionic content for corrosion resistance, good adhesion properties, and stable material properties even after long exposures within operating environments typically required of electronic devices. As a result of the above properties of its constituents, the polymer-based material of this invention is able to maintain desirable electrical insulation and thermal conduction properties when used as an adhesive, potting compound or encapsulation material for a wide variety of electronic devices, including IC chips and other power-dissipating devices that are mounted to a heat sink for thermal management.
Other objects and advantages of this invention will be better appreciated from the following detailed description.